Systems and methods for cascading photovoltaic structures

ABSTRACT

A string-forming system is described. The string-forming system may include at least a first cell-lifting mechanism and a second cell-lifting mechanism that can automatically arrange a set of strips of a photovoltaic structure into a cascaded formation. During operation, a controller can cause the first cell-lifting mechanism to lift a first strip from a first platform, and can cause the second cell-lifting mechanism to lift, from the first platform, a second strip that may follow the first strip on the first platform. The controller may then activate a first shifting actuator of the first cell-lifting mechanism or a second shifting actuator of the second cell-lifting mechanism to place a leading edge of the second strip above a trailing edge of the first strip.

CROSS-REFERENCE TO OTHER APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/866,776, filed Sep. 25, 2015, which claims the benefit of U.S.Provisional Patent Application No. 62/088,509, filed Dec. 5, 2014; andU.S. Provisional Patent Application No. 62/143,694, filed Apr. 6, 2015;the disclosures of which are incorporated herein by reference in theirentirety for all purposes.

This is related to U.S. patent application Ser. No. 14/563,867, AttorneyDocket Number P67-3NUS, entitled “HIGH EFFICIENCY SOLAR PANEL,” filedDec. 8, 2014; and U.S. patent application Ser. No. 14/510,008, AttorneyDocket Number P67-2NUS, entitled “MODULE FABRICATION OF SOLAR CELLS WITHLOW RESISTIVITY ELECTRODES,” filed Oct. 8, 2014; the disclosures ofwhich are incorporated herein by reference in their entirety for allpurposes.

FIELD OF THE INVENTION

This relates to solar panel fabrication, including cascading solar cellsto facilitate automated manufacturing of solar panels.

DEFINITIONS

“Solar cell” or “cell” is a photovoltaic structure capable of convertinglight into electricity. A cell may have any size and any shape, and maybe created from a variety of materials. For example, a solar cell may bea photovoltaic structure fabricated on a silicon wafer or one or morethin films on a substrate material (e.g., glass, plastic, or any othermaterial capable of supporting the photovoltaic structure), or acombination thereof

A “solar cell strip,” “photovoltaic strip,” or “strip” is a portion orsegment of a photovoltaic structure, such as a solar cell. A solar cellmay be divided into a number of strips. A strip may have any shape andany size. The width and length of a strip may be the same or differentfrom each other. Strips may be formed by further dividing a previouslydivided strip.

A “cascade” is a physical arrangement of solar cells or strips that areelectrically coupled via electrodes on or near their edges. There aremany ways to physically connect adjacent photovoltaic structures. Oneway is to physically overlap them at or near the edges (e.g., one edgeon the positive side and another edge on the negative side) of adjacentstructures. This overlapping process is sometimes referred to as“shingling.” Two or more cascading photovoltaic structures or strips canbe referred to as a “cascaded string,” or more simply as a string.

“Finger lines,” “finger electrodes,” and “fingers” refer to elongated,electrically conductive (e.g., metallic) electrodes of a photovoltaicstructure for collecting carriers.

A “busbar,” “bus line,” or “bus electrode” refers to an elongated,electrically conductive (e.g., metallic) electrode of a photovoltaicstructure for aggregating current collected by two or more finger lines.A busbar is usually wider than a finger line, and can be deposited orotherwise positioned anywhere on or within the photovoltaic structure. Asingle photovoltaic structure may have one or more busbars.

A “photovoltaic structure” can refer to a solar cell, a segment, orsolar cell strip. A photovoltaic structure is not limited to a devicefabricated by a particular method. For example, a photovoltaic structurecan be a crystalline silicon-based solar cell, a thin film solar cell,an amorphous silicon-based solar cell, a poly-crystalline silicon-basedsolar cell, or a strip thereof.

BACKGROUND

Advances in photovoltaic technology, which are used to make solarpanels, have helped solar energy gain mass appeal among those wishing toreduce their carbon footprint and decrease their monthly energy costs.However, the panels are typically fabricated manually, which is atime-consuming and error-prone process that makes it costly tomass-produce reliable solar panels.

Solar panels typically include one or more strings of complete solarcells. Adjacent solar cells in a string may overlap one another in acascading arrangement. For example, continuous strings of solar cellsthat form a solar panel are described in U.S. patent application Ser.No. 14/510,008, filed Oct. 8, 2014 and entitled “Module Fabrication ofSolar Cells with Low Resistivity Electrodes,” the disclosure of which isincorporated herein by reference in its entirety. Producing solar panelswith a cascaded cell arrangement can reduce the resistance due tointer-connections between the strips, and can increase the number ofsolar cells that can fit into a solar panel.

One method of making such a panel includes sequentially connecting thebusbars of adjacent cells and combining them. One type of panel (asdescribed in the above-noted patent application) includes a series ofcascaded strips created by dividing complete solar cells into strips,and then cascading the strips to form one or more strings.

Precise and consistent division of solar cells into strips and alignmentof strips or cells when forming a cascade arrangement is critical toensure proper electrical and physical connections, but such alignmentcan be difficult to reliably achieve in high volumes if performedmanually.

SUMMARY

Embodiments of the invention are directed to systems and methods forprecision automation of cascaded panel assembly by utilizing automatedelectro-mechanical systems that act in concert to manufacture cascadedsolar panels.

Several embodiments are described to allow one of ordinary skill in theart to appreciate the general subject matters that this specificationcovers. For ease of reading, not every possible variation and/orembodiment is covered in this section. Therefore, this summary shouldnot be construed to limit the scope of the invention.

One embodiment of the invention provides a string-forming system thatcan automatically arrange a set of strips into a cascaded formation. Thestring-forming system can include a controller that can control a numberof actuators and mechanical systems. During operation, the controllercan activate a first lifting actuator of a first cell-lifting mechanismso that the first cell-lifting mechanism may lift a first strip from afirst platform. The controller may also activate a second liftingactuator of a second cell-lifting mechanism so that the secondcell-lifting mechanism may lift, from the first platform, a second stripthat may follow the first strip on the first platform. The controllermay then activate a first shifting actuator of the first cell-liftingmechanism or a second shifting actuator of the second cell-liftingmechanism to place a leading edge of the second strip above a trailingedge of the first strip, while moving the first and second strips towarda second platform.

In a variation of this embodiment, the second strip can overlap thefirst strip by approximately two millimeters.

In a variation of this embodiment, the first and second cell-liftingmechanisms may each include at least one suction cup that can maintain asuction-hold on a strip.

In a variation of this embodiment, the first cell-lifting mechanism canlift the first strip to a first elevation, and the second cell-liftingmechanism can lift the second strip to a second elevation that may behigher than the first elevation.

In a variation of this embodiment, the controller can activate the firstand second lifting actuators so that they may rest the first and secondstrip on the second platform, where the leading edge of the second stripmay be placed above the trailing edge of the first strip.

In a variation of this embodiment, when placing the leading edge of thesecond strip above the trailing edge of the first strip, the controllercan activate the first shifting actuator to move the first cell-liftingmechanism toward the second cell-lifting mechanism and place the firststrip under the second strip.

In a variation of this embodiment, when placing the leading edge of thesecond strip above the trailing edge of the first strip, the controllercan activate the second shifting actuator to move the secondcell-lifting mechanism toward the first cell-lifting mechanism and placethe second strip over the first strip.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows a string-forming system, according to one embodiment ofthe invention.

FIG. 1B shows one example of a photovoltaic structure before beingdivided into multiple strips, according to an embodiment of theinvention.

FIG. 1C shows a close-up view of suction cups lifting a set of cascadedstrips, according to one embodiment of the invention.

FIG. 2A shows a photovoltaic structure, according to one embodiment ofthe invention.

FIG. 2B shows a cross-sectional view of a photovoltaic structure priorto being cleaved, according to one embodiment of the invention.

FIG. 2C shows a cascaded arrangement of three strips after aphotovoltaic structure is cleaved, according to one embodiment of theinvention.

FIG. 2D shows an exemplary conductive grid and blank space pattern onthe front surface of a photovoltaic structure, according to oneembodiment.

FIG. 2E shows an exemplary conductive grid and blank space pattern onthe back surface of a photovoltaic structure, according to oneembodiment of the invention.

FIG. 2F shows multiple strips, which are the result of separating aphotovoltaic structure along a set of grooves, according to oneembodiment of the invention.

FIG. 3 shows a sequence of steps for processing photovoltaic structuresto produce a string, according to one embodiment of the invention.

FIG. 4 shows a string-generating lane, according to one embodiment ofthe invention.

FIG. 5 shows an exemplary control apparatus, according to one embodimentof the invention.

FIG. 6 presents a flow chart illustrating a method for arranging stripsin a cascaded arrangement to form a string, according to one embodimentof the invention.

FIG. 7A shows a string-forming system, according to one embodiment ofthe invention.

FIG. 7B shows the string-forming system after lifting a set of strips,according to one embodiment of the invention.

FIG. 7C shows the string-forming system overlapping strips to form acascaded formation, according to one embodiment of the invention.

FIG. 7D shows strips in a cascaded formation, according to oneembodiment of the invention.

FIG. 8A shows one string assembly that is placed on a flat surface,according to one embodiment of the invention.

FIG. 8B shows a plurality of strips arranged to form a string assembly,according to one embodiment of the invention.

FIG. 8C shows a set of strips with alternating elevations, according toone embodiment of the invention.

FIG. 8D shows a string formed from strips with alternating elevations,according to one embodiment of the invention.

In the figures, like reference numerals refer to the same figureelements.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the embodiments, and is provided in the contextof a particular application and its requirements. Various modificationsto the disclosed embodiments will be readily apparent to those skilledin the art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present disclosure. Thus, the invention is not limited tothe embodiments shown, but is to be accorded the widest scope consistentwith the principles and features disclosed herein.

Overview

A string-forming system is provided that automatically arranges multiplephotovoltaic structure strips into a cascaded arrangement that forms astring, without significantly damaging the photovoltaic structures. Thestring-forming system can operate within an automated assembly line thatcan manufacture complete solar panels that may include multiple stringsof cascaded strips.

The string-forming system can obtain strips from a cleaving table, andin some embodiments, can arrange these strips into a cascadedarrangement while transporting the strips toward a flat surface that isto hold the string, such as an annealing platform. If a string ofcascaded strips are resting on the flat surface, the string-formingsystem can extend the string by placing the new cascaded striparrangement near the trailing end of the string. Later stages of thesolar-panel assembly line may combine multiple of these strings toproduce a solar panel.

FIG. 1A illustrates a string-forming system 102, according to oneembodiment of the invention. String-forming system 102 can include oneor more mechanical arms that can lift and move strips. For example,mechanical arms 104, 106, and 108 can each include a set of suction cups(e.g., suction cup 112) that can hold onto a strip by applying a suctionforce on a surface of the strip (e.g., an upward-facing surface ofstrips 114, 116, and 118). The suction force allows the strip to attachto the suction cups. Using suction cups can obviate the need formechanical clamps, which could damage the strip's electrodes and/orphotovoltaic structure. In some embodiments, the suction may be appliedto the base layer of the strip (e.g., the upward-facing layer of strips114, 116, and 118) to avoid applying forces to the strip's thin emitterlayer. This allows string-forming system 102 to prevent causingsignificant damage to the strip's emitter layer.

Mechanical arms 104, 106, and 108 can be mounted on a mount 110 that canslide laterally along a rail (not shown), for example, to move strips114, 116, and 118 from a holding tray to annealing platform 120. In someembodiments, mount 110 can also be coupled to an actuator (not shown)that can conform string-forming system 102 to a target elevation, suchas by raising or lowering string-forming system 102 to an elevation nearthe holding tray. This can allow string-forming system 102 to raisemechanical arms 104, 106, and 108 to a sufficient height to pick up aset of strips from the holding tray that may be elevated above annealingplatform 120. It will be understood by those skilled in the art thatalthough FIG. 1A shows an annealing platform 120 as the surface thatholds the cells, any surface may be used instead of an annealingplatform.

Mechanical arms 104, 106, and 108 can each include a set of actuatorsthat allow the mechanical arm to move a strip along an X and/or Y axisindependent of strips held by the other mechanical arms. For example,mechanical arm 106 can include an actuator that can lift center strip116, and mechanical arms 104 and 108 can include actuators that can liftand shift side strips 114 and 118, respectively. Once strips 114, 116,and 118 are above their target resting position along the X axis,mechanical arms 104, 106, and 108 can lower the strips along the Y axisto rest them on platform 120. The strips' final resting position canhave strip 114 overlap a trailing edge of strip 122 by a sufficientdistance that can cause their busbars to overlap, such as byapproximately 2 mm.

In one variation, the actuators that move mechanical arms 104, 106, and108 may be electric motors, which can be activated by a set ofelectronic motor controllers. In another variation, the actuators may bepneumatic or hydraulic actuators. String-forming system 102 can includea set of pneumatic or hydraulic pumps that can generate the air or fluidpressure necessary for moving each actuator to a target position.String-forming system 102 can also include a set of hoses (not shown)for transferring the air or fluid pressure to the actuators onmechanical arms 104, 106, and 108.

FIG. 1B shows one example of a photovoltaic structure before beingdivided into multiple strips, according to one embodiment of theinvention. Photovoltaic structure 128 in this example can include N typelightly doped crystalline silicon (c-Si) base layer 130, intrinsictunneling layer 132, N type heavily doped amorphous silicon (a-Si)surface field layer 134, transparent conductive oxide (TCO) layer 136,and front-side busbar 138. On the backside, the structure can includeintrinsic tunneling layer 140, P type a-Si emitter layer 142, TCO layer144, and backside busbar 146. The backside tunneling junction, formed byP type a-Si emitter layer 140, intrinsic tunneling layer 140, and N typec-Si base layer 130, can transport away the majority carriers generatedby base layer 130. The front side tunneling junction, formed by N typeheavily doped a-Si surface field layer 134, intrinsic tunneling layer132, and base layer 130, can transport away the minority carriersgenerated by base layer 130, thereby reducing the amount of carrierrecombination in base layer 130. Tunneling layers 132 and 140 canpassivate the interface between base layer 130 and the two heavily dopeda-Si layers while still allowing carriers generated by base layer 130 toenter these a-Si layers due to tunneling effect.

The tunneling junction between base layer 130 and emitter layer 142 iswhere the majority carriers are removed. It is therefore preferable thatdamage to this interface is kept small, such as damage caused byscribing groove 148, handling photovoltaic structure 128, or cleavingphotovoltaic structure 128 along groove 148 to produce strips 152 and154 (e.g., by producing cleave 150). For example, any impact made to thedownward-facing surface of strips 152 and 154 can create scratches ormicro cracks along TCO layer 144, a-Si layer 142, and/or tunneling layer140. It is therefore preferable to lift strips 152 and 154 by using aset of suction cups that apply a suction force on the top surface ofstrips 152 and 154 (e.g., on TCO 136). More details of an exemplaryphotovoltaic structure are provided in U.S. patent application Ser. No.13/601,441, filed Aug. 31, 2012, entitled “BACK JUNCTION SOLAR CELL WITHTUNNEL OXIDE,” the disclosure of which is hereby incorporated byreference in its entirety herein.

Exemplary photovoltaic structure 128 shown in FIG. 1B includes an N typelightly doped c-Si base layer. In general, the base layer can be eitherN or P type doped, or undoped, and can be made of a variety ofmaterials, including c-Si, a-Si, poly-crystalline silicon, ornon-silicon materials. Various device structures and designs based ondifferent materials can also be used to construct the photovoltaicstructure. For example, the photovoltaic structure can be a wafer-basedphotovoltaic structure, or a thin film photovoltaic structure, whichmight have a size and shape different from those of regular wafers.Preferred embodiments of the present invention provide a system that canassemble strips 152 and 154 in a cascaded arrangement without causingsignificant damage to busbars 138 and 146, or to the interface betweenthe base layer and emitter layer. Specifically, when strips 152 and 154are in a cascaded arrangement, busbar 146 of strip 154 can makeelectrical contact with busbar 138 of strip 152. A conductive paste canbind busbars 138 and 146 together to hold the cascaded arrangement.

Some conventional solar panels include a single string of seriallyconnected un-cleaved photovoltaic structures. As described in U.S.patent application Ser. No. 14/563,867, it can be more desirable to havemultiple (such as 3) strings, each string including cascaded strips, andconnect these strings in parallel. Such a multiple-parallel-string panelconfiguration provides the same output voltage with a reduced internalresistance. In general, a photovoltaic structure can be divided into nstrips, and a panel can contain n strings, each string having the samenumber of strips as the number of regular photovoltaic structures in aconventional single-string panel. Such a configuration can ensure thateach string outputs approximately the same voltage as a conventionalpanel. The n strings can then be connected in parallel to form a panel.As a result, the panel's voltage output can be the same as that of theconventional single-string panel, while the panel's total internalresistance can be 1/n of the resistance of a string (note that the totalresistance of a string made of a number of strips can be a fraction ofthe total resistance of a string made of the same number of undividedphotovoltaic structures). Therefore, in general, the greater n is, thelower the total internal resistance of the panel is, and the more powerone can extract from the panel. However, a tradeoff is that as nincreases, the number of connections required to inter-connect thestrings also increases, which increases the amount of contactresistance. Also, the greater n is, the more strips a singlephotovoltaic structure needs to be divided into, which increases theassociated production cost and decreases overall reliability due to thelarger number of strips used in a single panel.

Another consideration in determining n is the contact resistance betweenthe electrode and the photovoltaic structure on which the electrode isformed. The greater this contact resistance is, the greater n might needto be to reduce effectively the panel's overall internal resistance.Hence, for a particular type of electrode, different values of n mightbe needed to attain sufficient benefit in reduced total panel internalresistance to offset the increased production cost and reducedreliability. For example, conventional silver-paste or aluminum basedelectrode may require n to be greater than 4, because the process ofscreen printing and firing silver paste onto a photovoltaic structuredoes not produce ideal resistance between the electrode and theunderlying photovoltaic structure. In some embodiments of the presentinvention, the electrodes, including both the busbars and finger lines,can be fabricated using a combination of physical vapor deposition (PVD)and electroplating of copper as an electrode material. The resultingcopper electrode can exhibit lower resistance than an aluminum orscreen-printed-silver-paste electrode. Consequently, a smaller n can beused to attain the benefit of reduced panel internal resistance. In someembodiments, n is selected to be three, which is less than the n valuegenerally needed for photovoltaic structures with silver-pasteelectrodes or other types of electrodes. Correspondingly, two groovescan be scribed on a single photovoltaic structure to allow it to bedivided to three strips.

In addition to lower contact resistance, electro-plated copperelectrodes can also offer better tolerance to micro cracks, which mayoccur during a cleaving process. Such micro cracks might adverselyimpact silver-paste-electrode photovoltaic structures. Plated-copperelectrode, on the other hand, can preserve the conductivity across thesurface of the photovoltaic structure even if there are micro cracks inthe photovoltaic structure. The copper electrode's higher tolerance formicro cracks allows one to use thinner silicon wafers to manufacture thephotovoltaic structures. As a result, the grooves to be scribed on aphotovoltaic structure can be shallower than the grooves scribed on athicker wafer, which in turn helps increase the throughput of thescribing process. More details on using copper plating to formlow-resistance electrode on a photovoltaic structure are provided inU.S. patent application Ser. No. 13/220,532, filed Aug. 29, 2011,entitled “SOLAR CELL WITH ELECTROPLATED GRID,” the disclosure of whichis incorporated by reference in its entirety.

FIG. 1C shows a close-up view of suction cups lifting a set of cascadedstrips, according to one embodiment of the invention. Each mechanicalarm can include a number of suction cups that together can distributesufficient suction force across the top surface of a strip to lift thestrip. For example, mechanical arm 104 may include at least threesuction cups that each can apply suction to a different point along thetop surface of strip 114. In some embodiments, mechanical arm 104 caninclude four suction cups (e.g., suction cups 160), which can bearranged in two parallel rows with two suction cups per row to provide anear-equal suction force near each corner of an elongated strip.

String-forming system 102 can rest strips 114, 116, and 118 on platform120 in a cascaded arrangement, so that a busbar on the bottom surface ofstrip 114 comes in electrical contact with busbar 162 on a top surfaceof strip 122. For example, recall that strip 122 can have a conductivepaste deposited along busbar 162. This conductive paste may be anadhesive that can bond strip 114 and strip 122 together to resistseparation, and can also have conductive properties that can allow anelectric current to flow between busbar 162 and the busbar on the bottomsurface of strip 114 via the conductive paste.

In some embodiments, the busbar on strip 114 can be soldered to busbar162. However, one technical advantage in connecting the busbars via aconductive paste is that it can allow the string to be more flexible.Once deployed, solar panels can go through “thermal cycling” during a24-hour period as the temperature changes throughout the day. Thethermal cycling can exert pressure on the structure of the cascadedstrips. The conductive paste can allow the string to withstand thestructural stress that may be caused by the thermal cycling.

In some embodiments, the busbars may have an internal channel that canform a recessed surface inside the busbars, and can act as a receptacleto house a viscous adhesive. In some other embodiments, the busbars mayhave several grooves that may be formed via a mask at the time thebusbar is formed on the surface of the photovoltaic structure. Each setof grooves can be placed on a location within the busbar where thefingers intersect the busbar. Each of the grooves can act as areceptacle that can contain the conductive paste. When the two stripsare “cascaded,” the channels and/or grooves inside each busbar can forma housing that may keep the conductive paste within the boundary of thebusbars, and may prevent an overflow from the sides.

FIG. 2A shows photovoltaic structure 200, according to one embodiment ofthe invention. Photovoltaic structure 200 can include three photovoltaicstrips 202.1, 202.2, and 202.3, which can be the result of photovoltaicstructure 200 having an electroplated copper electrode that exhibits lowcontact resistance. Each strip can include a number of substantiallyparallel finger lines, such as finger lines 206, arranged in the Xdirection. These finger lines can collect the carriers generated by thephotovoltaic structure and allow them to move toward a busbar. Thebusbar can be any electrically conductive element such as a metallicstrip, often wider than a finger line, arranged in the Y direction. Thebusbar then can aggregate the current collected by the finger lines.Each strip can include two busbars, one on each surface, positioned onopposite edges. For example, strip 202.1 can have busbar 204.1 on thetop surface, and busbar 205.1 on the bottom surface. Similarly, strip202.2 can have busbars 204.2 and 205.2 on the top and bottom surfaces,respectively, and strip 202.3 can have busbars 204.3 and 205.3 on thetop and bottom surfaces, respectively. In one embodiment, photovoltaicstructure 200 can be scribed near and along busbars 204.1 and 204.2,which allows photovoltaic structure 200 to be subsequently cleaved intothree strips along these grooves. Additional busbars may be added toeither surface to reduce resistance.

FIG. 2B shows a cross-sectional view of photovoltaic structure 200 priorto being cleaved, according to one embodiment of the invention. Twoscribed grooves can be located between busbars 204.1 and 205.2, andbetween busbars 204.2 and 205.3, respectively. These grooves correspondto the cleave positions. After the subsequent cleaving process, theentire photovoltaic structure can be divided, for example, to threestrips 202.1, 202.2, and 202.3.

FIG. 2C shows a cascaded arrangement of three strips after aphotovoltaic structure is cleaved, according to one embodiment of theinvention. In this example, three strips 202.1, 202.2, and 202.3 can bearranged in a cascaded manner, such that the positive-side busbar of onestrip overlaps and is electrically coupled to the negative-side busbarof the neighboring strip. A conductive paste can be applied between twofacing busbars to facilitate both low-resistance contact and physicalbonding. Because no conductive tabs or wires are used, such a cascadingarrangement can reduce the series resistance due to inter-connectionbetween to strips, and can improve the fill-factor of the panel.

FIG. 2D shows an exemplary conductive grid and blank space pattern onthe front surface of a photovoltaic structure, according to oneembodiment of the invention. In the example shown in FIG. 2D, conductivegrid 220 can be made of any electrically conductive material, includingmetallic and non-metallic materials. Conductive grid 220 can includethree sub-grids, such as sub-grid 221. The photovoltaic structure canalso include a blank space (i.e., space not covered by electrodes)between neighboring sub-grids, such as blank space 225. The blank spaceprovides the area where scribing and cleaving can occur. Because theblank space is not covered with any conductive material, the scribingand cleaving can occur without contacting the electrode. Each sub-gridcan function as the front-side grid for the corresponding strip. Hence,this sub-grid-and-blank-space configuration can allow the photovoltaicstructure to be divided into three strips. In general, a respectivesub-grid can have various types of patterns. For example, a sub-grid canhave two, instead of one, busbars, or a single busbar placed in thecenter of the strip. In the example shown in FIG. 2D, the sub-grids caneach have a single busbar pattern placed on the edge, which allows thestrips to be cascaded.

FIG. 2E shows an exemplary conductive grid and blank space pattern onthe back surface of a photovoltaic structure, according to oneembodiment of the invention. In this example, back conductive grid 230can include three sub-grids. In one embodiment, the back side sub-gridsmay correspond to the front side sub-grids. As a result, the back sideof the strips can also absorb light to generate electrical energy,thereby allowing the solar panel to operate in a bifacial manner. In theembodiment shown in FIGS. 2D and 2E, the front and back side sub-gridscan have similar patterns except that the front and back edge-busbarsare located near opposite edges of the strip. In other words, the busbaron the front side of the strip may be located near one edge, and thebusbar on the back side may be located near the opposite edge. Inaddition, the locations of the blank spaces on the back side may bealigned with the locations of the blank spaces on the front side, suchthat the conductive grid lines may not interfere with the subsequentcleaving process.

In the embodiment shown in FIGS. 2D and 2E, each sub-grid may include anedge-busbar running along the longer edge of the corresponding strip anda plurality of parallel finger lines running in a directionsubstantially parallel to the shorter edge of the strip. For example, inFIG. 2D, sub-grid 221 may include edge-busbar 222, and a number offinger lines, such as finger lines 223 and 224. A blank space, which isnot covered by any conductive material, can be placed between twoadjacent sub-grids to facilitate the subsequent scribe and cleavingprocess. Note that in FIG. 2D the ends of the finger lines can beconnected by a conductive line to form “loops.” This type of “looped”finger line pattern can reduce the likelihood of the finger lines frompeeling away from the photovoltaic structure after a long period ofusage. For example, as shown in FIG. 2D, finger lines 223 and 224 areconnected by conductive line 226 to form a loop with rounded corners.Optionally, the sections where the finger lines are joined can be widerthan the rest of the finger lines to provide more durability and preventpeeling. Other finger line patterns, such as un-looped straight lines orloops with different shapes, are also possible.

As shown in FIG. 2D, strip-shaped blank space 225, shown in a shadedrectangle, can separate sub-grid 221 from its adjacent sub-grid. Thewidth of the blank space, such as blank space 225, is chosen to providesufficient area for the scribing process (e.g., using a laser scribesystem) without causing significant damage to the nearby electrodes, andyet sufficiently narrow so that the electrodes can reach the edge ofeach strip and provide low-resistance collection of the carriers. Theremay be a tradeoff between a wider blank space that facilitates moreerror-tolerant scribing operation and a narrower blank space thatresults in more effective current collection. In one embodiment, theblank space width can be between 0.5 mm and 2 mm. In a furtherembodiment, the width of such a blank space may be 1 mm.

As mentioned above, in order to prevent damaging the emitter junction ofthe photovoltaic structure, the scribing operation may be performed onthe surface corresponding to the surface field layer. For example, ifthe emitter junction is on the front side of the photovoltaic structure,the scribing may occur to the back surface of the photovoltaicstructure. On the other hand, if the emitter junction is on the backside, the scribing may occur on the front surface of the photovoltaicstructure. FIG. 2F shows multiple strips 252.1, 252.2, and 252.3, whichare the result of separating a photovoltaic structure along a set ofgrooves, according to one embodiment of the invention. Each strip caninclude two busbars, one on each side, on opposite edges. For example,strip 252.1 can include separate busbars 254.1 and 254.2 on the frontside and back side, respectively.

String-Forming System

FIG. 3 shows a sequence of steps for processing photovoltaic structuresto produce a string, according to one embodiment of the invention. Inthis example, conveyor 310 can move photovoltaic structures to scribingsystem 302, which can scribe one or more grooves along the busbars ofeach photovoltaic structure. Conveyor 310 can then move the photovoltaicstructures to adhesive-dispensing system 304, which can dispense aconductive adhesive paste on busbars of the strips, so that aftercleaving these strips can be bonded together in a cascaded arrangement.

After application of the conductive adhesive paste, the photovoltaicstructures can be picked up from conveyor 310 by, for example, a roboticarm (not shown) via a suction device that may be integrated into therobotic arm. The robotic arm can hold the photovoltaic structure bymaintaining the suction force while moving the photovoltaic structuretoward cleaving system 306. The robotic arm can rotate photovoltaicstructures approximately 90 degrees before placing it onto a loadingsystem of cleaving system 306. The loading system may also include abuffer where the photovoltaic structures can be stored before beingmoved to cleaving system 306.

Cleaving system 306 can receive photovoltaic structures from the loadingsystem, and can divide the photovoltaic structures into strips along thegrooves formed by scribing tool 302. After a photovoltaic structure isdivided into a number of (e.g., three) strips, string-arrangement system308 can lift these strips and arrange the strips in a cascadedarrangement while moving the strips to annealing platform 312.String-arrangement system 308 can overlap a leading edge of the threecascaded strips over the trailing edge of string 314, thereby extendingstring 314.

The sequence of operations shown in FIG. 3 is one of many ways tomanufacture cascaded strings. For example, the step of applying theconductive adhesive paste can occur before scribing or after cleaving.Furthermore, a variety of apparatuses and systems can be used toimplement the functions showing in FIG. 3.

FIG. 4 shows string-generating lane 400, according to one embodiment ofthe invention. String-forming system 402 can pick up a set of stripsfrom holding tray 404, and determines whether these strips have passedan electrical test. For example, holding tray 404 may reside on acleaving table that can include a cleaving apparatus, and can include atesting apparatus that may test electrical properties of the strips todetermine whether they have become damaged during or prior to thecleaving process. If any of the strips fail the test, string-formingsystem 402 can discard the entire photovoltaic structure (e.g., thethree strips) by depositing the strips into disposal tray 414.

In some embodiments, string-forming system 402 can test electricalproperties of the strips while the strips are on holding tray 404, orwhile moving the strips toward annealing platform 416. For example, eachmechanical arm can have a probe that can apply a predetermined voltageto a busbar on the strip being tested, and the same probe or anotherprobe can perform current measurements to test the strip. A defectivestrip can then be identified based on the current measured by theprobes. A strip may be considered defective if a measured currentthrough the strip is less than a predetermined minimum current, whichcan occur when micro cracks form along the busbars or when thephotovoltaic structure may have become damaged.

In one variation, the strips may be placed on a grounded surface (e.g.,holding tray 404) that can make contact with another busbar on the strip(e.g., a busbar on a bottom surface of the strip). The electricalcurrent may flow from the busbar on the top surface of the strip towardthe other busbar, and to the grounded surface. In another variation,each mechanical arm may also include a grounded probe that can groundanother busbar of the strip (e.g., another busbar on a top surface orbottom surface of the strip). In this variation, the mechanical arm cantest the strip while moving the cascaded strip toward annealing platform416.

If the strips pass the test, string-forming system 402 can lift, shiftand align the strips to form a cascaded strip assembly, and can placethe cascaded strip assembly on annealing platform 416 to form or extendstring 418. For example, string-forming system 402 can be mounted onrail 406, and rail 406 can itself be mounted on another rail 410. Topick up strips from holding tray 404, actuator 412 can movestring-forming system 402 (e.g., laterally) along rail 410 towardholding tray 404, and actuator 408 can move (e.g., raise) string-formingsystem 402 along rail 406 so that its suction cups are elevated aboveholding tray 404. String-forming system 402 can then pick up the stripsby gently lowering its mechanical arms toward the strips, and activatinga pump to create a suction force at the suction cups.

Once the strips are secured to a bottom surface of the suction cups,actuator 408 and/or the actuators for the mechanical arms onstring-forming system 402 can raise the strips above holding tray 404.Actuator 412 can then move string-forming system 402 along rail 410toward a target location on platform 416, and actuator 408 can conformstring-forming system 402 to platform 416, such as by lowering it untilthe strips are substantially close to platform 416. String-formingsystem 402 can then extend string 420, for example, by overlapping onebusbar of the cascaded strip arrangement with another busbar near thetrailing end of string 418.

In some variations, string-forming system 402 can create the cascadedstrip arrangement while moving the strips toward their target restingposition on platform 416. Alternatively, string-forming system 402 canmove each individual strip toward platform 416, one strip at a time,such as by lowering the strips to create the cascaded strip arrangementwhile forming or extending string 418 one strip at a time.

In some embodiments, annealing platform 416 can move (e.g., laterally)to pass string 418 between two heat-treating surfaces of targetedannealing apparatus 420, which may apply heat to the areas of string 418where two strips overlap. Targeted annealing apparatus 420 may include aset of heat-treating bars that each can have a contact surface that maybe substantially flat. In some embodiments, the heat-treating bars maybe arranged as a set of bars above and a set of bars below platform 416.String 418 can be placed on the surface, which may have a series ofopenings that may allow the heat-treating bars to contact the stringfrom under the surface. The heat-treating bars can be positioned suchthat as they may approach the string, they may apply heat to the bothsides of the string around the area where two strips overlap. In someembodiments, the heat-treating bars can cure the overlapping areas ofthe strips up to 160° Celsius. The heat can cause the paste in betweentwo overlapping busbars to cure.

In some embodiments, the conductive paste may be in a form of a resinthat can include one or more types of conductive particles. Theconductive particles may be coated with a protection layer that canevaporate when the paste is thermally cured, and can thereby result inelectrical conductivity between the conductive particles suspendedinside the resin.

FIG. 5 shows exemplary control apparatus 500, according to oneembodiment of the invention. Apparatus 500 can include a computer-basedor electronic control system that can operate a string-forming system tocreate and extend a string of cascaded strips. For example, apparatus500 can include a plurality of modules which may communicate with oneanother via a wired or wireless communication channel. Apparatus 500 maybe realized using one or more integrated circuits, and may include feweror more modules than those shown in FIG. 5. Further, apparatus 500 maybe integrated in a computer system, or realized as a separate mechanismwhich may be capable of communicating with other computer systems and/ormechanisms.

Apparatus 500 can include processor 502, memory 504, and storage device506. Memory 504 can include a volatile memory (e.g., RAM) that serves asa managed memory, and can be used to store one or more memory pools. Insome embodiments, storage device 506 can store an operating system, andinstructions for monitoring and controlling the string-generatingprocess.

Apparatus 500 can also include actuator-controlling module 508,probe-testing module 510, position-computing module 512,platform-controlling module 514, and anneal-controlling module 516.Actuator-controlling module 508 can activate a set of actuators on amechanical arm to move the mechanical arm to a strip-holding tray on acleaving table. Probe-testing module 510 can perform a probe test onstrips, using a set of test probes on the cleaving table and/or on themechanical arm. If a strip fails the probe test, actuator-controllingmodule 508 can operate the mechanical arm to move the strips to adiscard tray. Otherwise, actuator-controlling module 508 can operate themechanical arm to transport the strips toward an annealing platform thatmay have a cascaded string on a top surface.

Position-computing module 512 can periodically re-compute an updatedposition of the cascaded string and/or the individual strips withrespect to a fixed point on the string-generating lane, while theplatform moves the string toward the lay-up station. For example,position-computing module 512 can calculate the position of a strip on amechanical arm based on a position of the string-forming system along arail, and a position of the mechanical arm's suction cups relative tothe string-forming system. Also, position-computing module 512 cancalculate the position of a strip on the annealing platform based on animage captured by a vision system, a corresponding time stamp, and thespeed of the platform.

Platform-controlling module 514 can activate a set of actuators that cancause the platform surface to move the cascaded string toward a lay-upstation that combines multiple strings of cascaded strips to form asolar panel. Anneal-controlling module 516 can control a set ofheat-treating bars to perform targeted annealing along the contactsurfaces between cascaded strips to cause a conductive paste to anneal.

FIG. 6 presents a flow chart illustrating method 600 for arrangingstrips in a cascaded arrangement to form a string, according to oneembodiment of the invention. During operation, a computer system thatcontrols the string-forming system can determine whether there are anystrips in a holding tray of the cleaving table (operation 602). If thereare no strips in the tray, the computer system can wait for apredetermined duration (operation 604) before returning to operation 602to check the holding tray.

On the other hand, if strips exist in the tray, the computer system cancontrol the string-forming system to pick up the strips from the holdingtray (operation 606), and can optionally determine probe test resultsfor the strips (operation 608). Recall that in some embodiments, thecleaving table can include a probe tester that tests various electricalproperties of the individual strips. In some other embodiments, thestring-forming system can include a set of test probes that can performthe test on the individual strips either while the strips rest on theholding tray, or after picking up the strips from the holding tray.

If the computer system determines that the strips did not pass the probetest (operation 610), the computer system can configure thestring-forming system to move the strips toward a discard tray, and todiscard of the strips in the discard tray (operation 612). In someembodiments, during operation 606, the computer system can cause thestring-forming system to pick up the strips, for example, by activatinga suction pump to create a negative air pressure on a set of suctioncups. This negative air pressure can create a suction hold on a topsurface of a strip, which can press the strip against a bottom surfaceof the suction cups. To discard the strips in the discard tray, thecomputer system can deactivate the negative air pressure for the suctioncups that hold a given strip when the strip is elevated above thediscard tray, and/or can activate a pressure pump to cause a positiveairflow at the suction cups.

Otherwise, if the strips have passed the probe test, the computer systemcan operate the string-forming system to arrange the strips into acascading arrangement (operation 614), and can move the string-formingsystem toward an annealing platform (operation 616) eithersimultaneously or as a separate operation.

The computer system can also determine whether a partial string existson the platform (operation 618). If a partial string does not exist, thecomputer system can operate the string-forming system to deposit thecascaded strip arrangement (which is being carried by the string-formingsystem) onto the platform to start a new string (operation 620).Otherwise, the computer system can operate the string-forming system tooverlap a leading busbar of the cascaded strip arrangement with atrailing busbar of the string on the platform (operation 622).

The computer system may then determine whether the string on theplatform may be complete (operation 624). If the string has not reacheda target length or does not include a target number of strips, thecomputer system can return to operation 602 to add one or more strips tothe string's cascaded arrangement. Otherwise, the computer system canactivate the platform to move the string toward a lay-up station(operation 626), and the process can end. In some embodiments, thecomputer system can cause the platform to move the string toward thelay-up station while performing operations 602-624 to from the string.Moreover, while moving the string toward the lay-up station, theplatform can move the string through a targeted-annealing apparatus thatcan heat the string around the areas where two strips overlap to cureconductive paste between the overlapping strips.

FIG. 7A shows string-forming system 700, according to one embodiment ofthe invention. String-forming system 700 can include mechanical arm 708on the left side, mechanical arm 706 on the right side, and mechanicalarm 704 in between mechanical arms 706 and 708. Each mechanical arm canhave one or more suction cups 710, which may lift a strip from holdingtray 712 (e.g., an output tray from a cleaving table).

In one embodiment, each of the mechanical arms may be capable of movingin the vertical direction and/or in the horizontal direction. Eachmechanical arm can lift the strips from tray 712 via the suction cupsthat apply a holding force to the surface of the strips. The suctioncups can have a matching elevation to distribute the holding forceevenly across the top surface of the strips, which can prevent causingsignificant damage to the strips. For example, the even holding forceacross a strip's surface can prevent warping the strip due to torsion,which would otherwise damage the strip's photovoltaic structure or coulddamage the copper busbars or fingerlines across the surface of thestrip. A respective mechanical arm can lift the strip it is holding to apredetermined elevation, and as a result, may create a cascadedformation (e.g., a stepped formation).

FIG. 7B shows string-forming system 700 after lifting a set of strips,according to one embodiment of the invention. Mechanical arm 708 canlift strip 728 to a height that can clear a sidewall of tray 712,mechanical arm 708 can lift strip 727 to a height that may be higherthan that of strip 728, and mechanical arm 706 can lift strip 726 to aheight that may be higher than that of strip 726.

String-forming system 700 may control the movement of the mechanicalarms in a number of ways. In one embodiment, the movement of themechanical arms along the X axis and Y axis may be controlled by afirmware that can control the movement of each mechanical arm from afirst three-dimensional coordinate to a second three-dimensionalcoordinate. In another embodiment, string-forming system 700 may beretrofitted with a vision system that can measure the distance of eachmechanical arm with respect to another mechanical arm, or any otherreference point, and may provide near real-time feedback to a controlmodule that can direct the movement of the mechanical arm. In anotherembodiment, any combination of the above-noted methods may be used, inaddition to other methods of movement control, to direct the movement ofthe mechanical arms and achieve the desired level of precision.

Mechanical arms 704, 706, and 708 can each include an actuator (e.g.,actuator 718) that can conform a strip to a predetermined elevation inthe Y direction, such as by raising or lowering the strip. In someembodiments, mechanical arm 704 may maintain the strip at a fixedposition in the X direction (relative to string-forming system 700),while mechanical arms 706 and 708 can each include another actuator(e.g., actuator 720) that can shift a strip laterally in the Xdirection. For example, in one embodiment, mechanical arm 708 caninclude one or more actuators 720 that each can include pneumatic orhydraulic cylinders that may push or pull suction cups 710 in the Xdirection. In another embodiment, actuators 720 can include an electricmotor that can extend or contract a shaft that shifts suction cups inthe X direction. Mechanical arms 706 and 708 can also include at leastone set of linear ball bushings, which can stabilize the lateralmovement of mechanical arms 706 and 708.

In one embodiment, mechanical arms 706 and 708 move toward mechanicalarm 704 by a predetermined distance until the strips overlap. Thepredetermined distance may be about 2 millimeters in one embodiment,which may correspond to the width of the busbar on each strip.

FIG. 7C shows string-forming system 700 overlapping strips 724, 726, and728 to form a cascaded formation, according to one embodiment of theinvention. Specifically, string-forming system 700 can activate actuator720 that can cause mechanical arm 706 to move strip 728 along direction732 toward strip 724, and can activate another actuator 721 which cancause mechanical arm 706 to move strip 726 along direction 730 towardstrip 724.

When the strips are overlapped by the appropriate distance (e.g.,distance 740), string-forming system 700 can activate actuators for eachof mechanical arms 704, 706, and 708 (e.g., actuator 718) to move, suchas by lowering, strips 724, 726, and 728 onto a substantially flatsurface. Placing the strips onto the surface can cause the conductivepaste on each busbar to bind the busbars of the overlapped strips, whichthen forms the cascaded strip assembly.

In one variation, string-forming system 700 can form the cascaded stripformation by depositing each individual strip on a location of the flatsurface under the mechanical arms. For example, mechanical arm 708 mayfirst place strip 728 on the flat surface to overlap the string assemblyon the flat surface, and then mechanical arm 704 may overlap strip 724over strip 728 on the flat surface by overlap distance 740. Then,mechanical arm 706 may place strip 726 on the flat surface, so thatstrip 726 can overlap the string assembly on the flat surface by overlapdistance 740. In another variation, string-forming system 700 can formthe cascaded formation while the strips are elevated over the flatsurface (e.g., while in transit from the cleaving table). The mechanicalarms of the string-forming system 700 may then shift the strips untilachieving the appropriate amount of overlap with respect to the stringassembly on the flat surface. String-forming system 700 may then placethe cascaded strips onto the flat surface to extend the length of thestring.

In one embodiment, string-forming system 700 may have more mechanicalarms such that an entire string may be formed during one cycle. In thisembodiment, the mechanical arms can lift the strips, create a cascadedformation while the strips are lifted, move the strips to achieve aproper amount of overlap, and place the strips on the flat surface toform a string. In another embodiment, the process may be divided intomultiple sub-processes such that two or more strips may be lifted andaligned to form a partial cascaded string, and the partial string maythen be lifted and aligned with another partial string to form acomplete cascaded string.

FIG. 7D shows strips 724, 726, and 728 in a cascaded formation,according to one embodiment of the invention. Every three strips can beformed into a cascaded strip assembly, and may be placed on anothercascaded strip assembly on the flat surface. Repeating this process canextend a string of cascaded strips.

FIG. 8A shows one string assembly 802 that is placed on flat surface806, according to one embodiment of the invention. Another cascadedstrip assembly 804 can also be placed on top of string assembly 802 toform a longer string. As shown in FIG. 8A, cascaded strip assembly 804can also overlap string assembly 802 by overlap distance 808.

FIG. 8B shows a plurality of strips arranged to form string assembly820, according to one embodiment of the invention.

FIG. 8C shows a set of strips with alternating elevations, according toone embodiment of the invention. Instead of a continuous steppedformation, the string-forming system may cascade strips 850 so that theymay overlap on two edges of one surface. This configuration may need adifferent conductive grid pattern where each strip can have two busbarson one side to accommodate the alternating-elevation configuration.

For example, cascaded assembly 852 can include three strips, so that twoouter strips are bonded to busbars on a top-facing surface of the centerstrip. In one embodiment, the string-forming system may place cascadedassembly 852 on flat surface 858, so that the two outer strips ofcascaded assembly 852 may overlap strip 854 and strip 852 that rest onflat surface 858.

In another embodiment, the string-forming system may build a string byadding an even number of cascaded strips at a time to the string. Forexample, the string-forming system can arrange two strips in a cascadedassembly whose leading strip has a higher elevation than the trailingstrip of the cascaded assembly. The leading strip can include busbars onits downward-facing surface, so that an exposed busbar may be bonded toan upward-facing busbar of the string on the flat surface. Once thecascaded assembly is added to the string, the trailing strip of thecascaded assembly may rest on the flat surface, with an exposed busbaron its upward-facing surface near its trailing edge. The next cascadedassembly may then be bonded to this exposed busbar.

FIG. 8D shows string 870 formed from strips with alternating elevations,according to one embodiment of the invention. One advantage of thealternating-elevation configuration may be that a string may not requirea tab at one end. Given that the opposite polarities of the string maybe accessible from one side, the need for a tab may be eliminated.

The data structures and code described in this detailed description cantypically be stored on a computer-readable storage medium, which may beany device or medium that can store code and/or data for use by acomputer system. The computer-readable storage medium can include, butis not limited to, volatile memory, non-volatile memory, magnetic andoptical storage devices such as disk drives, magnetic tape, CDs (compactdiscs), DVDs (digital versatile discs or digital video discs), or othermedia capable of storing computer-readable media now known or laterdeveloped.

The methods and processes described in the detailed description sectioncan be embodied as code and/or data, which can be stored in acomputer-readable storage medium as described above. When a computersystem reads and executes the code and/or data stored on thecomputer-readable storage medium, the computer system can perform themethods and processes embodied as data structures and code and storedwithin the computer-readable storage medium.

Furthermore, the methods and processes described above can be includedin hardware modules. For example, the hardware modules can include, butare not limited to, application-specific integrated circuit (ASIC)chips, field-programmable gate arrays (FPGAs), and otherprogrammable-logic devices now known or later developed. When thehardware modules are activated, the hardware modules can perform themethods and processes included within the hardware modules.

The foregoing descriptions of embodiments of the invention have beenpresented for purposes of illustration and description only. They arenot intended to be exhaustive or to limit the invention to the formsdisclosed. Accordingly, many modifications and variations may beapparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the invention. The scope of theinvention is defined by the appended claims.

What is claimed is:
 1. A method, comprising: activating a first liftingactuator operable to lift a first cascaded strip assembly from a firstplatform, wherein the first cascaded strip assembly comprises two ormore cascaded strips; activating a second lifting actuator operable tolift a second cascaded strip assembly from the first platform, whereinthe second cascaded strip assembly comprises two or more cascadedstrips; and activating a first shifting actuator of the first celllifting actuator or a second shifting actuator of the second celllifting actuator to overlap a leading edge of the second cascaded stripassembly with a trailing edge of the first cascaded strip assembly. 2.The method of claim 1, wherein the first cascaded strip assemblycomprises two outer strips and a center strip, wherein busbars of thetwo outer strips are bonded to busbars on a first surface of the centerstrip.
 3. The method of claim 1, wherein the first cascaded stripassembly comprises a first and a second outer strip and a center strip,wherein a first busbar of the first outer strip is bonded to a secondbusbar on a first surface of the center strip, and a third busbar of thesecond outer strip is bonded to a fourth busbar on a second surface,opposite the first surface, of the center strip.
 4. The method of claim1, further comprising: controlling actuators of the first liftingactuator and the second lifting actuator to place the first cascadedstrip assembly and the second cascaded strip assembly on a secondplatform, wherein a leading edge of the first cascaded strip assemblyoverlaps a trailing edge of a third cascaded strip assembly resting onthe second platform to extend a string comprising the third cascadedstrip assembly.
 5. The method of claim 1, further comprising:maintaining a suction-hold on each strip of the first cascaded stripassembly via suction cups of the first cell lifting actuator.
 6. Themethod of claim 1, further comprising: activating the first cell liftingactuator and the second cell lifting actuator to place the leading edgeof the second cascaded strip assembly to overlap the trailing edge ofthe first cascaded strip assembly by approximately two millimeters. 7.The method of claim 1, wherein the first platform and the secondplatform correspond to a surface area of a conveyer belt.
 8. A method,comprising: activating a first lifting actuator operable to lift a firstcascaded strip assembly from a first platform, wherein the firstcascaded strip assembly comprises two or more cascaded strips;activating a first shifting actuator of the first cell lifting actuatorto overlap a leading edge of the first cascaded strip assembly with atrailing edge of a string of cascaded strips on a second platform inorder to extend the string.
 9. The method of claim 8, wherein before thestring is extended, the string comprises at least two cascaded strips.10. The method of claim 8, wherein the first cascaded strip assemblycomprises two outer strips and a center strip, wherein busbars of thetwo outer strips are bonded to busbars on a first surface of the centerstrip.
 11. The method of claim 8, wherein the first cascaded stripassembly consists of two overlapped strips, and wherein the stripcomprises a plurality of strips with alternating elevations.
 12. Themethod of claim 8, wherein the first cascaded strip assembly comprises afirst and a second outer strip and a center strip, wherein a firstbusbar of the first outer strip is bonded to a second busbar on a firstsurface of the center strip, and a third busbar of the second outerstrip is bonded to a fourth busbar on a second surface, opposite thefirst surface, of the center strip.
 13. The method of claim 8, furthercomprising maintaining a suction-hold on each strip of the firstcascaded strip assembly via suction cups of the first cell liftingactuator.
 14. The method of claim 8, further comprising, activating thefirst cell lifting actuator to place the leading edge of the firstcascaded strip assembly to overlap a trailing edge of the string byapproximately two millimeters.
 15. The apparatus of claim 1, wherein thesecond platform corresponds to a surface area of a conveyer belt.
 16. Asystem for forming a string of cascading solar cells, the systemcomprising: a first mechanical arm configured to move at least in afirst direction, wherein the first mechanical arm includes at least asuction-cup at one end and configured to apply a holding force to asurface; and wherein the first mechanical arm lifts a first cascadedstrip assembly of solar cells from a first platform surface, and thefirst mechanical arm aligns the first cascaded strip assembly topartially overlap a second cascaded strip assembly of solar cells on asecond platform surface to extend a string of solar cells.
 17. Thesystem of claim 16, wherein the first cascaded strip assembly comprisestwo outer strips and a center strip, wherein busbars of the two outerstrips are bonded to busbars on a first surface of the center strip. 18.The system of claim 16, wherein the first cascaded strip assemblycomprises a first and a second outer strip and a center strip, wherein afirst busbar of the first outer strip is bonded to a second busbar on afirst surface of the center strip, and a third busbar of the secondouter strip is bonded to a fourth busbar on a second surface, oppositethe first surface, of the center strip.
 19. The system of claim 16,wherein the first cascaded strip assembly consists of two overlappedstrips, and wherein the second cascaded strip assembly comprises aplurality of strips with alternating elevations.
 20. The system of claim16, wherein the second platform surface is a conveyer belt.